a) Field of the Invention
The present invention relates to a testing and calibrating device for optical eye length measurement devices.
b) Description of the Related Art
A spherical transparent test body which is preferably made of glass, has coatings and a refractive index of approximately 2 is known as a testing and calibrating device for optical eye length measurement instruments (EP-A 509903, U.S. Pat. No. 5,347,327, U.S. Pat. No. 5,347,328) from DE 19504465 A1 by the present Applicant. The coating, chiefly of the back of the test body, involves a costly technique and difficult technology.
Therefore, the primary object of the present invention is a test body for optical eye length measurement devices that is simple to produce but is universally applicable.
In accordance with the invention, a testing and calibrating device for optical eye length measurement devices comprises two plano-convex lenses which are arranged in the illumination beam path so as to be oppositely oriented. A neutral filter with a defined transmission is located between these two plano-convex lenses.